1. Field of the Invention
The present invention relates to a piston/cylinder assembly for a reciprocating compressor.
2. Prior Art
As illustrated in FIG. 7 and 8, a conventional reciprocating compressor used generally for compressing a refrigerant in a refrigerating system is comprised of a driving motor 160 having a stator 163, a rotor 161 and a rotor shaft 165, and a cylinder assembly 200 having a cylinder 139, a piston 120 and a cylinder head 150.
The cylinder head 150 has a suction chamber 151 through which the refrigerant is supplied from the outside and a discharge chamber 152 through which the refrigerant compressed in the cylinder 139 is discharged out of the compressor. Between the cylinder head 150 and the cylinder 139 is interposed a valve seat 111 and a suction valve plate 101. The valve seat 111 is provided with a suction port 117 and a discharge port 115 which are connected to the suction chamber 151 and the discharge chamber 152 of the cylinder head 150, respectively. The discharge port 115 is elastically shut tight by a the discharge valve reed 113 which seats on the valve seat 111 and likewise a suction port 117 is elastically sealed off by the suction valve reed 103 formed on the suction valve plate 101.
When the compressor is activated, the driving motor runs, turning the crank shaft 165 whose resulting rotation is transferred to the piston 120 by means of a connecting rod 131 and changed to a reciprocating movement of the piston 120 in the cylinder 139.
The movement of the piston 120 from the upper dead point to the lower dead point is accompanied with a drop in the pressure of the cylinder compartment. This causes the suction valve reed 103 to bend toward the inner side of the cylinder 139 and results in the opening of the suction port 117 while discharge port 115 is closed off by the discharge valve reed 113. As a consequence, the refrigerant is sucked into the cylinder 139 from the suction chamber 151. In a similar fashion, the movement of the piston 120 from the lower dead point to the upper dead point results in an increase in the pressure inside the cylinder 139. The discharge valve reed 113, as a result, bends toward the outer side of the cylinder 139 to open up the discharge port 115. At this time, the suction port 117 is sealed off by the suction valve reed 103. Consequently, the refrigerant in the cylinder 139 is compressed and discharged to the discharge chamber 152. The refetition of the above process is the mechanism by which the refrigerant is compressed.
At the upper dead point of the piston 120, a gap of about 0.2 mm thick separates the piston 120 and the suction valve plate 101. A larger gap would result in a decrease in the efficiency of the compressor as the compressed high-pressure refrigerant leaves a larger amount of residue inside the cylinder 139. In other words, the high-pressure residual refrigerant expands again as the piston 120 moves from the upper to the lower dead point, and the suction valve reed 103 does not open up until the pressures inside the cylinder 139 and outside the suction valve plate 101 are made equal. The amount of refrigerant intake is therefore much reduced.
However, too small a gap between the piston 120 and the suction valve plate 101 could damage the suction valve plate 101 or the the suction valve reed 103 formed therein from the shocks coming from the high-pressure refrigerant and the refrigerant-oil mixture as the piston 120 move toward the upper dead point. Since the clearance gap between the suction valve plate 101 and the piston shall be determined by a comprimise between the compression efficiency and the suction valve plate's 101 shock tolerance, there's a definite limit to the realizable minimum clearance.
Therefore, it is an object of this invention to provide a cylinder assembly for a reciprocating compressor which has a minimum clearance gap between the piston and the suction valve plate so as to reduce the amount of residual refrigerant whose subsequent expansion lowers the compression efficiency, and yet which reduces the risk of damage to the suction valve plate and reed by the high-pressure refrigerant and oil-refrigerant mixture.